Polymers, resist compositions and patterning process

ABSTRACT

A polymer having fluorinated vinyl phenol units copolymerized with acrylonitrile units has high transmittance to VUV radiation. A resist composition using the polymer as a base resin has high sensitivity and resolution to high-energy radiation and good plasma etching resistance and is suited for lithographic microprocessing.

[0001] This invention relates to polymers useful as the base resin inchemical amplification resist compositions suited for microfabrication.It also relates to chemical amplification resist compositions comprisingthe polymers, and a patterning process using the same.

BACKGROUND OF THE INVENTION

[0002] In the drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. The rapid advancetoward finer pattern rules is grounded on the development of aprojection lens with an increased NA, a resist material with improvedperformance, and exposure light of a shorter wavelength. In particular,the change-over from i-line (365 nm) to shorter wavelength KrF laser(248 nm) brought about a significant innovation, promising a possibilityof commercial manufacture of devices on 0.10 micron rule. To the demandfor a resist material with a higher resolution and sensitivity,acid-catalyzed chemical amplification positive working resist materialsare effective as disclosed in U.S. Pat. Nos. 4,491,628 and 5,310,619(JP-B 2-27660 and JP-A 63-27829). They now become predominant resistmaterials especially adapted for deep UV lithography.

[0003] Resist materials adapted for KrF excimer lasers enjoyed early useon the 0.3 micron process, went through the 0.25 micron rule, andcurrently entered the mass production phase on the 0.18 micron rule.Engineers have started investigation on the 0.15 micron rule, with thetrend toward a finer pattern rule being accelerated. With a wavelengthreduction from KrF to ArF laser (193 nm), it is expected to enableminiaturization of the design rule to 0.13 μm or less. Sinceconventionally used novolac resins and poly(vinyl phenol) resins havevery strong absorption in proximity to 193 nm, they cannot be used asthe base resin for resists. To ensure transparency and dry etchingresistance, some engineers investigated acrylic and alicyclic (typicallycycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A9-230595 and WO 97/33198.

[0004] With respect to F₂ excimer laser (157 nm) which is expected toenable further miniaturization to 0.10 μm or less, more difficultyarises in insuring transparency because it was found that acrylic resinsare not transmissive to light at all and those cycloolefin resins havingcarbonyl bonds have strong absorption. It was also found that poly(vinylphenol) is somewhat improved in transmittance near 160 nm, but far belowthe practical level. It was found that reducing carbonyl andcarbon-to-carbon double bonds is essential for insuring a transmittance.

[0005] Under the circumstances, there is a need for a resist compositionwhich performs well upon exposure to radiation having a wavelength below180 nm.

SUMMARY OF THE INVENTION

[0006] An object of the invention is to provide a novel polymer having ahigh transmittance to vacuum ultraviolet radiation below 300 nm,especially F₂ excimer laser beam (157 nm), Kr₂ excimer laser beam (146nm), KrAr excimer laser beam (134 nm) and Ar₂ excimer laser beam (121nm), and useful as the base resin in a chemical amplification resistcomposition. Another object is to provide a chemical amplificationresist composition comprising the polymer, and a patterning processusing the same.

[0007] It has been found that using as the base resin a polymer havingfluorinated vinyl phenol units copolymerized with acrylonitrile units, aresist material featuring high transparency and etching resistance isobtained.

[0008] The invention is predicated on the finding below. Phenolicpolymers exhibit superior etching resistance and alkali solubility toacrylic polymers. Among others, halogenated, especially fluorinatedphenolic polymers have significant transmittance-improving effects,affording a practically acceptable transmittance. Polyacrylonitrile isrelatively transparent to wavelengths in the F₂ region and has higheretching resistance than acrylic polymers. Then copolymerization offluorinated hydroxystyrene with polyacrylonitrile can improvetransparency without sacrificing etching resistance.

[0009] In one aspect, the invention provides a polymer comprisingrecurring units of the following general formula (1).

[0010] Herein R¹, R², R³ and R⁵ each are independently hydrogen,fluorine, or a straight, branched or cyclic alkyl or fluorinated alkylgroup of 1 to 20 carbon atoms, R⁴ is an acid labile group, letters a, band c are numbers satisfying 0≦a<5, 0≦b<5, 0<a+b<5 and 0<c<5, and m andn are positive numbers.

[0011] In another aspect, the invention provides a resist compositioncomprising the polymer. In a preferred embodiment, the inventionprovides a chemically amplified, positive resist composition comprising(A) the polymer, (B) an organic solvent, and (C) a photoacid generator.In further preferred embodiments, the resist composition furtherincludes (D) a basic compound and/or (E) a dissolution inhibitor.

[0012] In a further aspect, the invention provides a process for forminga resist pattern comprising the steps of applying the resist compositiononto a substrate to form a coating; heat treating the coating and thenexposing it to high-energy radiation having a wavelength of up to 300 nmor electron beam through a photo mask; and optionally heat treating theexposed coating and developing it with a developer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] Polymer

[0014] According to the invention, the polymer or high molecular weightcompound is defined as comprising recurring units of the followinggeneral formula (1).

[0015] Herein R¹, R², R³ and R⁵ each are independently hydrogen,fluorine, or a straight, branched or cyclic alkyl or fluorinated alkylgroup of 1 to 20 carbon atoms. R⁴ is an acid labile group.

[0016] The straight, branched or cyclic alkyl groups represented by R¹,R², R³ and R⁵ are those of 1 to 20 carbon atoms, preferably 1 to 12carbon atoms, and more preferably 1 to 10 carbon atoms, includingmethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-octyl. The fluorinatedalkyl groups correspond to the foregoing alkyl groups in which some orall of the hydrogen atoms are replaced by fluorine atoms and include,for example, trifluoromethyl, 2,2,2-trifluoroethyl,3,3,3-trifluoropropyl, and 1,1,2,2,3,3,3-heptafluoropropyl.

[0017] The acid labile group represented by R⁴ is selected from avariety of such groups, preferably from among the groups of thefollowing formulas (2) and (3), tertiary alkyl groups with 4 to 40carbon atoms of the following formula (4), trialkylsilyl groups whosealkyl groups each have 1 to 6 carbon atoms, and oxoalkyl groups of 4 to20 carbon atoms.

[0018] In formula (2), R⁶ is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group whosealkyl groups each have 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms or a group of formula (4). Exemplary tertiary alkyl groupsare tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-5-oxooxoran-4-yl. Letter “a” is an integer of 0 to 6.

[0019] In formula (3), R⁷ and R⁸ are independently hydrogen or straight,branched or cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to10 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl andn-octyl. R⁹ is a monovalent hydrocarbon group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, which may have a hetero atom (e.g.,oxygen atom), for example, straight, branched or cyclic alkyl groups,and such groups in which some hydrogen atoms are replaced by hydroxyl,alkoxy, oxo, amino or alkylamino groups. Illustrative examples of thesubstituted alkyl groups are given below.

[0020] A pair of R⁷ and R⁸, a pair of R⁷ and R⁹, or a pair of R⁸ and R⁹,taken together, may form a ring. Each of R⁷, R⁸ and R⁹ is a straight orbranched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms, when they form a ring.

[0021] Illustrative examples of the acid labile groups of formula (2)include tert-butoxycarbonyl, tert-butoxy-carbonylmethyl,tert-amyloxycarbonyl, tert-amyloxycarbonyl-methyl,1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonylmethyl,1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyloxycarbonylmethyl,1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydro-furanyloxycarbonylmethyl.

[0022] Of the acid labile groups of formula (3), illustrative examplesof the straight or branched groups are given below.

[0023] Of the acid labile groups of formula (3), illustrative examplesof the cyclic groups include tetrahydrofuran-2-yl,2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl and2-methyltetrahydropyran-2-yl. Preferred among the groups of formula (3)are ethoxyethyl, butoxyethyl and ethoxypropyl.

[0024] In formula (4), R¹⁰, R¹¹ and R¹² are independently monovalenthydrocarbon groups, for example, straight, branched or cyclic alkylgroups of 1 to 20 carbon atoms, which may contain a hetero atom such asoxygen, sulfur, nitrogen or fluorine. A pair of R¹⁰ and R¹¹, a pair ofR¹⁰ and R¹², or a pair of R¹¹ and R¹², taken together, may form a ring.Each of R¹⁰, R¹¹ and R¹² is a straight or branched alkylene group of 3to 20 carbon atoms, preferably 4 to 16 carbon atoms, when they form aring.

[0025] Examples of the tertiary alkyl group represented by formula (4)include tert-butyl, triethylcarbyl, 1-ethylnorbornyl,1-methylcyclohexyl, 1-ethylcyclopentyl, 2-(2-methyl)adamantyl,2-(2-ethyl)adamantyl, and tert-amyl.

[0026] Other illustrative examples of the tertiary alkyl group are givenbelow as formulae (4-1) through (4-16).

[0027] Herein, R¹³ and R¹⁴ each are a straight, branched or cyclic alkylgroup of 1 to 6 carbon atoms, for example, methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, cyclopropyl,cyclopropylmethyl or cyclohexyl. R¹⁵ is hydrogen, a monovalent C1-6hydrocarbon group which may contain a hetero atom or a monovalent C1-6hydrocarbon group which may be separated by a hetero atom, with thehydrocarbon being typically alkyl. The hetero atom is an oxygen, sulfuror nitrogen atom, which is contained or intervenes in the form of —OH,—OR, —O—, —S—, —S(═O)—, —NH₂, —NHR, —NR₂, —NH—, or —NR— wherein R is analkyl group of 1 to 20 carbon atoms, and especially 1 to 16 carbonatoms.

[0028] R¹⁶ is hydrogen or an alkyl, hydroxyalkyl, alkoxy or alkoxyalkylgroup of 1 to 20 carbon atoms, especially 1 to 16 carbon atoms, whichmay be straight, branched or cyclic. Illustrative examples includemethyl, hydroxymethyl, ethyl, hydroxyethyl, propyl, isopropyl, n-butyl,sec-butyl, n-pentyl, n-hexyl, methoxy, methoxymethoxy, ethoxy, andtert-butoxy.

[0029] Of the acid labile group represented by R⁴, the trialkylsilylgroups whose alkyl groups each have 1 to 6 carbon atoms includetrimethylsilyl, triethylsilyl, and tert-butyldimethylsilyl.

[0030] The oxoalkyl groups of 4 to 20 carbon atoms include3-oxocyclohexyl and groups of the following formulae.

[0031] Alternatively, the acid labile group represented by R⁴ may be acrosslinking group of the following general formula (5a) or (5b). Inthis embodiment, the polymer is crosslinked between molecules or withina molecule with the crosslinking groups.

[0032] Herein, R¹⁹ and R²⁰ each are hydrogen or a straight, branched orcyclic alkyl group of 1 to 8 carbon atoms, or R¹⁹ and R²⁰, takentogether, may form a ring, with the proviso that each of R¹⁹ and R²⁰ isa straight or branched alkylene group of 1 to 8 carbon atoms when theyform a ring. R²¹ is a straight, branched or cyclic alkylene group of 1to 10 carbon atoms. Letter b and d each are 0 or an integer of 1 to 10,preferably 0 or an integer of 1 to 5, and c is an integer of 1 to 7. Ais a (c+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbonatoms, which may have an intervening hetero atom and in which thehydrogen atom attached to a carbon atom may be partially replaced by ahydroxyl group, carboxyl group, carbonyl group or fluorine atom. B is—CO—O—, —NHCO—O— or —NHCONH—.

[0033] Preferably, A is a di- to tetra-valent straight, branched orcyclic alkylene, alkyltriyl or alkyltetrayl group of 1 to 20 carbonatoms or arylene group of 6 to 30 carbon atoms, which may have anintervening hetero atom and in which the hydrogen atom attached to acarbon atom may be partially replaced by a hydroxyl group, carboxylgroup, acyl group or halogen atom. Letter c is preferably an integer of1 to 3.

[0034] As understood from the value of c in formula (5a) or (5b), thecrosslinking group is not limited to a divalent one and trivalent tooctavalent groups are acceptable. For example, the divalent crosslinkinggroup is exemplified by groups of the following formulas (5a′) and(5b′), and the trivalent crosslinking group is exemplified by groups ofthe following formulas (5a″) and (5b″).

[0035] “A” in the crosslinking group is described in more detail. The(c+1)-valent organic groups represented by A include hydrocarbon groups,for example, substituted or unsubstituted alkylene groups having 1 to 50carbon atoms, especially 1 to 40 carbon atoms, substituted orunsubstituted arylene groups having 6 to 50 carbon atoms, morepreferably 6 to 40 carbon atoms, a combination of an alkylene group andan arylene group, and c′-valent groups obtained by eliminating onehydrogen atom attached to a carbon atom from the foregoing groupswherein c′ is an integer of 3 to 8; and (c+1)-valent heterocyclicgroups, and a combination of such a heterocyclic group with any one ofthe foregoing hydrocarbon groups. In the alkylene and arylene groups, ahetero atom such as O, NH, N(CH₃), S and SO₂ may intervene and wheresubstituted, the substituent is a hydroxyl, carboxyl, acyl group orfluorine.

[0036] Illustrative examples of A are given below.

[0037] Preferably, in formula (5a), R¹⁹ is methyl, R²⁰ is hydrogen, b is0, c is 1, and A is ethylene, 1,4-butylene or 1,4-cyclohexylene.

[0038] The polymer which is crosslinked between molecules and/or withina molecule with crosslinking groups having C—O—C linkages can besynthesized by reacting a corresponding uncrosslinked polymer with analkenyl ether in the presence of an acid catalyst in a conventional way.

[0039] Where decomposition of other acid labile groups takes place underthe acid catalyzed condition, the alkenyl ether is previously reactedwith hydrochloric acid or the like to form a halogenated alkyl ether,which is reacted with the uncrosslinked polymer under basic conditionsin a conventional way, obtaining the end product.

[0040] Illustrative, non-limiting examples of the alkenyl ether includeethylene glycol divinyl ether, triethylene glycol divinyl ether,1,2-propanediol divinyl ether, 1,3-propanediol divinyl ether,1,3-butanediol divinyl ether, 1,4-butanediol divinyl ether,tetramethylene glycol divinyl ether, neopentyl glycol divinyl ether,trimethylolpropane trivinyl ether, trimethylolethane trivinyl ether,hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether,1,4-divinyloxymethyl cyclohexane, pentaerythritol divinyl ether,pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether,sorbitol tetravinyl ether, sorbitol pentavinyl ether, ethylene glycoldiethylene vinyl ether, triethylene glycol diethylene vinyl ether,ethylene glycol dipropylene vinyl ether, triethylene glycol diethylenevinyl ether, trimethylolpropane triethylene vinyl ether,trimethylol-propane diethylene vinyl ether, pentaerythritol diethylenevinyl ether, pentaerythritol triethylene vinyl ether, pentaerythritoltetraethylene vinyl ether, and compounds of the formulas (I-1) to (I-31)given below.

[0041] Also included are diethylene vinyl ether terephthalate,diethylene vinyl ether phthalate, diethylene vinyl ether isophthalate,dipropylene vinyl ether phthalate, dipropylene vinyl etherterephthalate, dipropylene vinyl ether isophthalate, diethylene vinylether maleate, diethylene vinyl ether fumarate, and diethylene vinylether itaconate, and compounds of the formulas (II-1) to (II-11) givenbelow. The alkenyl ether is not limited to the exemplified compounds.

[0042] Referring back to formula (1), subscripts m and n are positivenumbers, satisfying the range: 0<n/(n+m)<1 and 0<m/(n+m)<1, preferably0.1<n/(n+m)<0.9 and 0.1<m/(n+m)<0.9, and more preferably 0.2<n/(n+m)<0.8and 0.2<m/(n+m)<0.8.

[0043] In addition to the recurring units of formula (1), the inventivepolymer may contain less than 50 mol %, especially less than 40 mol % ofrecurring units of the formula (6a) or (6b) shown below, or recurringunits originating from methacrylic acid derivatives, acrylic acidderivatives, malonic acid derivatives, itaconic acid derivatives, vinylalcohol derivatives, maleic anhydride derivatives or maleimidederivatives.

[0044] In formula (6a) or (6b), R¹, R², R³, a and b are as definedabove, and d is a number in the range: 0<d<5.

[0045] The polymer of the invention is generally synthesized by mixingmonomers of the following formulae (1a) and (1b) to afford therespective units with a solvent, adding a catalyst thereto, andeffecting polymerization reaction while heating or cooling the system ifnecessary. The polymerization reaction depends on the type of initiatoror catalyst, trigger means (including light, heat, radiation andplasma), and polymerization conditions (including temperature, pressure,concentration, solvent, and additives). Commonly used for polymerizationthe polymer of the invention are radical polymerization of triggeringpolymerization with radicals of 2,2′-azobisisobutyronitrile (AIBN) orthe like, and ion (anion) polymerization using catalysts such as alkyllithium. The polymerization reaction can be effected in a conventionalway.

[0046] Desirably the polymer has a weight average molecular weight ofabout 2,000 to about 1,000,000, and especially about 3,000 to about100,000.

[0047] The polymer of the invention can be used as a base resin inresist compositions, specifically chemical amplification type resistcompositions, and especially chemical amplification type positiveworking resist compositions.

[0048] Resist Composition

[0049] In a preferred embodiment, the chemically amplified positiveresist composition is defined as comprising (A) the polymer (base resin)defined above, (B) an organic solvent, and (C) a photoacid generator. Inthe resist composition, there may be further formulated (D) a basiccompound and/or (E) a dissolution inhibitor.

[0050] Component (B)

[0051] The organic solvent used as component (B) in the invention may beany organic solvent in which the photoacid generator, base resin(inventive polymer), dissolution inhibitor, and other components aresoluble. Illustrative, non-limiting, examples of the organic solventinclude ketones such as cyclohexanone and methyl-2-n-amylketone;alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol,1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propyleneglycol monomethyl ether, ethylene glycol monomethyl ether, propyleneglycol monoethyl ether, ethylene glycol monoethyl ether, propyleneglycol dimethyl ether, and diethylene glycol dimethyl ether; and esterssuch as propylene glycol monomethyl ether acetate, propylene glycolmonoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate,methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butylacetate, tert-butyl propionate, and propylene glycol mono-tert-butylether acetate. These solvents may be used alone or in combinations oftwo or more thereof. Of the above organic solvents, preferred arediethylene glycol dimethyl ether, 1-ethoxy-2-propanol and ethyl lactate,in which the photoacid generator is most soluble, and propylene glycolmonomethyl ether acetate which is safe, and mixtures thereof.

[0052] Component (C)

[0053] Suitable examples of the photoacid generator (C) include oniumsalts of general formula (7) below, diazomethane derivatives of formula(8), glyoxime derivatives of formula (9), β-ketosulfone derivatives,disulfone derivatives, nitrobenzylsulfonate derivatives, sulfonic acidester derivatives, and imidoyl sulfonate derivatives.

(R³⁰)_(b)M⁺K⁻  (7)

[0054] In the formula, R³⁰ is a straight, branched or cyclic alkyl of 1to 12 carbon atoms, an aryl of 6 to 12 carbon atoms, or an aralkyl of 7to 12 carbon atoms; M⁺ is iodonium or sulfonium; K⁻ is anon-nucleophilic counter-ion; and the letter b is 2 or 3.

[0055] Illustrative examples of alkyl groups represented by R³⁰ includemethyl, ethyl, propyl, butyl, cyclohexyl, 2-oxocyclohexyl, norbornyl,and adamantyl. Exemplary aryl groups include phenyl; alkoxyphenyl groupssuch as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl,p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groupssuch as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl,4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary aralkylgroups include benzyl and phenethyl. Examples of the non-nucleophiliccounter-ion represented by K⁻ include halide ions such as chloride andbromide; fluoroalkylsulfonate ions such as triflate,1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate;arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; andalkylsulfonate ions such as mesylate and butanesulfonate.

[0056] In the formula, R³¹ and R³² are straight, branched or cyclicalkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl orhalogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7to 12 carbon atoms.

[0057] Illustrative examples of alkyl groups represented by R³¹ and R³²include methyl, ethyl, propyl, butyl, amyl, cyclopentyl, cyclohexyl,norbornyl, and adamantyl. Exemplary halogenated alkyl groups includetrifluoromethyl, 1,1,1-trifluoroethyl, 1,1,1-trichloroethyl, andnonafluoro-butyl. Exemplary aryl groups include phenyl; alkoxyphenylgroups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl,ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; andalkylphenyl groups such as 2-methylphenyl, 3-methylphenyl,4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, anddimethylphenyl. Exemplary halogenated aryl groups include fluorobenzene,chlorobenzene, and 1,2,3,4,5-pentafluorobenzene. Exemplary aralkylgroups include benzyl and phenethyl.

[0058] In the formula, R³³, R³⁴, and R³⁵ are straight, branched orcyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, arylor halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of7 to 12 carbon atoms. R³⁴ and R³⁵ may together form a cyclic structurewith the proviso that if they form a cyclic structure, each is astraight or branched alkylene group of 1 to 6 carbon atoms.

[0059] The alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkylgroups represented by R³³, R³⁴, and R³⁵ are exemplified by the samegroups as mentioned above for R³¹ and R³². Examples of alkylene groupsrepresented by R³⁴ and R³⁵ include methylene, ethylene, propylene,butylene, and hexylene.

[0060] Illustrative examples of the photoacid generator include:

[0061] onium salts such as diphenyliodonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate,diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)phenyliodoniump-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)-sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate,tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate,triphenylsulfonium nonafluorobutane-sulfonate, triphenylsulfoniumbutanesulfonate, trimethyl-sulfonium trifluoromethanesulfonate,trimethylsulfonium p-toluenesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate,dimethylphenylsulfonium trifluoromethanesulfonate,dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfoniumtrifluoromethanesulfonate, and dicyclohexylphenylsulfoniump-toluenesulfonate;

[0062] diazomethane derivatives such asbis(benzenesulfonyl)-diazomethane, bis(p-toluenesulfonyl)diazomethane,bis(xylenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)-diazomethane,bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane,bis(isobutylsulfonyl)-diazomethane, bis(sec-butylsulfonyl)diazomethane,bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)-diazomethane,bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane,bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane,bis(tert-amylsulfonyl)-diazomethane,1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)-diazomethane,1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)-diazomethane, and1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane;

[0063] glyoxime derivatives such asbis-O-(p-toluene-sulfonyl)-α-dimethylglyoxime,bis-O-(p-toluenesulfonyl)-α-diphenylglyoxime,bis-O-(p-toluenesulfonyl)-α-dicyclohexyl-glyoxime,bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-O-(n-butanesulfonyl)-α-dimethylglyoxime,bis-O-(n-butanesulfonyl)-α-diphenylglyoxime,bis-O-(n-butanesulfonyl)-α-dicyclohexylglyoxime,bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime,bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-O-(methanesulfonyl)-α-dimethylglyoxime,bis-O-(trifluoromethanesulfonyl)-α-dimethylglyoxime,bis-O-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime,bis-O-(tert-butanesulfonyl)-α-dimethylglyoxime,bis-O-(perfluoro-octanesulfonyl)-α-dimethylglyoxime,bis-O-(cyclohexane-sulfonyl)-α-dimethylglyoxime,bis-O-(benzenesulfonyl)-α-dimethylglyoxime,bis-O-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime,bis-O-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime,bis-O-(xylenesulfonyl)-α-dimethylglyoxime, andbis-O-(camphorsulfonyl)-α-dimethylglyoxime;

[0064] β-ketosulfone derivatives such as2-cyclohexyl-carbonyl-2-(p-toluenesulfonyl)propane and2-isopropyl-carbonyl-2-(p-toluenesulfonyl)propane;

[0065] disulfone derivatives such as diphenyl disulfone and dicyclohexyldisulfone;

[0066] nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzylp-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;

[0067] sulfonic acid ester derivatives such as1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluene-sulfonyloxy)benzene; and

[0068] imidoyl sulfonate derivatives such as phthalimidoyl triflate,phthalimidoyl tosylate, 5-norbornene-2,3-dicarboxyimidoyl triflate,5-norbornene-2,3-dicarboxyimidoyl tosylate, and5-norbornene-2,3-dicarboxyimidoyl n-butylsulfonate.

[0069] Preferred among these photoacid generators are onium salts suchas triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, andtris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate; diazomethanederivatives such as bis(benzenesulfonyl)-diazomethane,bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(n-butylsulfonyl)-diazomethane, bis(isobutylsulfonyl)diazomethane,bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)-diazomethane,bis(isopropylsulfonyl)diazomethane, andbis(tert-butylsulfonyl)diazomethane; and glyoxime derivatives such asbis-O-(p-toluenesulfonyl)-α-dimethylglyoxime andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime. These photoacid generatorsmay be used singly or in combinations of two or more thereof. Oniumsalts are effective for improving rectangularity, while diazomethanederivatives and glyoxime derivatives are effective for reducing standingwaves. The combination of an onium salt with a diazomethane or aglyoxime derivative allows for fine adjustment of the profile.

[0070] The photoacid generator is preferably added in an amount of about0.2 to 15 parts by weight, and especially about 0.5 to 8 parts byweight, per 100 parts by weight of all the base resins. At less than 0.2part, the amount of acid generated during exposure would be too smalland the sensitivity and resolution be poor, whereas the addition of morethan 15 parts would lower the transmittance of the resist and result ina poor resolution.

[0071] Component (D)

[0072] The basic compound used as component (D) is preferably a compoundcapable of suppressing the rate of diffusion when the acid generated bythe photoacid generator diffuses within the resist film. The inclusionof this type of basic compound holds down the rate of acid diffusionwithin the resist film, resulting in better resolution. In addition, itsuppresses changes in sensitivity following exposure, thus reducingsubstrate and environment dependence, as well as improving the exposurelatitude and the pattern profile. See JP-A 5-232706, 5-249683, 5-158239,5-249662, 5-257282, 5-289322, and 5-289340.

[0073] Examples of suitable basic compounds include primary, secondary,and tertiary aliphatic amines, mixed amines, aromatic amines,heterocyclic amines, carboxyl group-bearing nitrogenous compounds,sulfonyl group-bearing nitrogenous compounds, hydroxyl group-bearingnitrogenous compounds, hydroxyphenyl group-bearing nitrogenouscompounds, alcoholic nitrogenous compounds, amide derivatives, and imidederivatives. Of these, aliphatic amines are especially preferred.

[0074] Examples of suitable primary aliphatic amines include ammonia,methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, pentylamine,tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine,heptylamine, octylamine, nonylamine, decylamine, dodecylamine,cetylamine, methylenediamine, ethylenediamine, andtetraethylenepentamine. Examples of suitable secondary aliphatic aminesinclude dimethylamine, diethylamine, di-n-propylamine,di-iso-propylamine, di-n-butylamine, di-iso-butylamine,di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine,dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, didodecylamine, dicetylamine,N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, andN,N-dimethyltetraethylenepentamine. Examples of suitable tertiaryaliphatic amines include trimethylamine, triethylamine,tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine,tri-iso-butylamine, tri-sec-butylamine, tripentylamine,tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, tridodecylamine,tricetylamine, N,N,N′,N′-tetramethylmethylenediamine,N,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N′-tetramethyl-tetraethylenepentamine.

[0075] Examples of suitable mixed amines include dimethylethylamine,methylethylpropylamine, benzylamine, phenethylamine, andbenzyldimethylamine. Examples of suitable aromatic and heterocyclicamines include aniline derivatives (e.g., aniline, N-methylaniline,N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline,3-methylaniline, 4-methylaniline, ethylaniline, propylaniline,trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline,2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, andN,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine,triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene,pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole,2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazolederivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g.,thiazole and isothiazole), imidazole derivatives (e.g., imidazole,4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazolederivatives, furazan derivatives, pyrroline derivatives (e.g., pyrrolineand 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine,N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone),imidazoline derivatives, imidazolidine derivatives, pyridine derivatives(e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine,butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine,trimethylpyridine, triethylpyridine, phenylpyridine,3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine,benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine,1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine,2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine),pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives,pyrazoline derivatives, pyrazolidine derivatives, piperidinederivatives, piperazine derivatives, morpholine derivatives, indolederivatives, isoindole derivatives, 1H-indazole derivatives, indolinederivatives, quinoline derivatives (e.g., quinoline and3-quinolinecarbonitrile), isoquinoline derivatives, cinnolinederivatives, quinazoline derivatives, quinoxaline derivatives,phthalazine derivatives, purine derivatives, pteridine derivatives,carbazole derivatives, phenanthridine derivatives, acridine derivatives,phenazine derivatives, 1,10-phenanthroline derivatives, adeninederivatives, adenosine derivatives, guanine derivatives, guanosinederivatives, uracil derivatives, and uridine derivatives.

[0076] Examples of suitable carboxyl group-bearing nitrogenous compoundsinclude aminobenzoic acid, indolecarboxylic acid, and amino acidderivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid,glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine,methionine, phenylalanine, threonine, lysine,3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples ofsuitable sulfonyl group-bearing nitrogenous compounds include3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples ofsuitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenylgroup-bearing nitrogenous compounds, and alcoholic nitrogenous compoundsinclude 2-hydroxypyridine, aminocresol, 2,4-quinolinediol,3-indolemethanol hydrate, monoethanolamine, diethanolamine,triethanolamine, N-ethyldiethanolamine, N,N-diethyl-ethanolamine,triisopropanolamine, 2,2′-iminodiethanol, 2-aminoethanol,3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine,2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine,1-[2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol,1-(2-hydroxyethyl)-pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone,3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol,8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidineethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, andN-(2-hydroxyethyl)-isonicotinamide. Examples of suitable amidederivatives include formamide, N-methylformamide, N,N-dimethylformamide,acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, andbenzamide. Suitable imide derivatives include phthalimide, succinimide,and maleimide.

[0077] In addition, basic compounds of the following general formulas(10) and (11) may also be included.

[0078] In the formulas, R⁴¹, R⁴², R⁴³, R⁴⁷ and R⁴⁸ independentlystraight, branched or cyclic alkylenes of 1 to 20 carbon atoms; R⁴⁴,R⁴⁵, R⁴⁶, R⁴⁹ and R⁵⁰ are hydrogen, alkyls of 1 to 20 carbon atoms, oramino; R⁴⁴ and R⁴⁵, R⁴⁵ and R⁴⁶, R⁴⁴ and R⁴⁶, R⁴⁴ with R⁴⁵ and R⁴⁶, andR⁴⁹ and R⁵⁰ may bond together to form rings; and S, T and U are eachintegers from 0 to 20, with the proviso that hydrogen is excluded fromR⁴⁴, R⁴⁵, R⁴⁶, R⁴⁹ and R⁵⁰ when S, T and U are equal to 0.

[0079] The alkylene groups represented by R⁴¹, R⁴², R⁴³, R⁴⁷ and R⁴⁸preferably have 1 to 20 carbon atoms, more preferably 1 to 10 carbonatoms, and most preferably 1 to 8 carbon atoms. Examples includemethylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene,n-pentylene, isopentylene, hexylene, nonylene, decylene, cyclopentylene,and cyclohexylene.

[0080] The alkyl groups represented by R⁴⁴, R⁴⁵, R⁴⁶, R⁴⁹ and R⁵⁰preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbonatoms, and most preferably 1 to 6 carbon atoms, and may be straight,branched or cyclic. Examples include methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, hexyl, nonyl, decyl,dodecyl, tridecyl, cyclopentyl, and cyclohexyl.

[0081] Where R⁴⁴ and R⁴⁵, R⁴⁵ and R⁴⁶, R⁴⁴ and R⁴⁶, R⁴⁴ with R⁴⁵ andR⁴⁶, and R⁴⁹ and R⁵⁰ form rings, the rings preferably have 1 to 20carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1to 6 carbon atoms, and may have pendant alkyl groups of 1 to 6 carbonatoms, and especially 1 to 4 carbon atoms.

[0082] S, T, and U are each integers from 0 to 20, preferably from 1 to10, and more preferably from 1 to 8.

[0083] Illustrative examples of the compounds of formulas (10) and (11)include tris{2-(methoxymethoxy)ethyl}amine,tris{2-(methoxyethoxy)ethyl}amine,tris[2-{(2-methoxy-ethoxy)methoxy}ethyl]amine,tris{2-(2-methoxyethoxy)-ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxypropoxy)-ethyl}amine,tris[2-{(2-hydroxyethoxy)ethoxy}ethyl]amine,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane,4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane,1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4,1-aza-15-crown-5, and 1-aza-18-crown-6. Especially preferred basiccompounds are tertiary amines, aniline derivatives, pyrrolidinederivatives, pyridine derivatives, quinoline derivatives, amino acidderivatives, hydroxyl group-bearing nitrogenous compounds, hydroxyphenylgroup-bearing nitrogenous compounds, alcoholic nitrogenous compounds,amide derivatives, imide derivatives,tris{2-(methoxymethoxy)ethyl}amine,tris{2-(2-methoxyethoxy)-ethyl}amine,tris[2-{(2-methoxyethoxy)methyl}ethyl]amine, and 1-aza-15-crown-5.

[0084] The above-described basic compound may be used singly or incombinations of two or more thereof, and is preferably formulated in anamount of about 0.01 to 2 parts, and especially about 0.01 to 1 part byweight, per 100 parts by weight of all the base resins. At less than0.01 part, the desired effects of the basic compound would not beapparent, while the use of more than 2 parts would result in too low asensitivity.

[0085] Component (E)

[0086] The dissolution inhibitor (E) is a compound with a molecularweight of up to 3,000 which changes its solubility in an alkalinedeveloper under the action of an acid. Typically, a compound obtained bypartially or entirely substituting acid labile substituents on a phenolor carboxylic acid derivative having a molecular weight of up to 2,500is added as the dissolution inhibitor.

[0087] Examples of the phenol or carboxylic acid derivative having amolecular weight of up to 2,500 include bisphenol A, bisphenol H,bisphenol S, 4,4-bis(4′-hydroxyphenyl)valeric acid,tris(4-hydroxyphenyl)methane, 1,1,1-tris(4′-hydroxyphenyl)ethane,1,1,2-tris(4′-hydroxyphenyl)ethane, phenolphthalein, andthimolphthalein. The acid labile substituents are the same as thoseexemplified as the acid labile groups in the polymer.

[0088] Illustrative, non-limiting, examples of the dissolutioninhibitors which are useful herein include

[0089] bis(4-(2′-tetrahydropyranyloxy)phenyl)methane,

[0090] bis(4-(2′-tetrahydrofuranyloxy)phenyl)methane,

[0091] bis(4-tert-butoxyphenyl)methane,

[0092] bis(4-tert-butoxycarbonyloxyphenyl)methane,

[0093] bis(4-tert-butoxycarbonylmethyloxyphenyl)methane,

[0094] bis(4-(1′-ethoxyethoxy)phenyl)methane,

[0095] bis(4-(1′-ethoxypropyloxy)phenyl)methane,

[0096] 2,2-bis(4′-(2″-tetrahydropyranyloxy))propane,

[0097] 2,2-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)propane,

[0098] 2,2-bis(4′-tert-butoxyphenyl)propane,

[0099] 2,2-bis(4′-tert-butoxycarbonyloxyphenyl)propane,

[0100] 2,2-bis(4-tert-butoxycarbonylmethyloxyphenyl)propane,

[0101] 2,2-bis(4′-(1″-ethoxyethoxy)phenyl)propane,

[0102] 2,2-bis(4′-(1″-ethoxypropyloxy)phenyl)propane,

[0103] tert-butyl 4,4-bis(4′-(2″-tetrahydropyranyloxy)phenyl)-valerate,

[0104] tert-butyl 4,4-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)-valerate,

[0105] tert-butyl 4,4-bis(4′-tert-butoxyphenyl)valerate,

[0106] tert-butyl 4,4-bis(4′-tert-butoxycarbonyloxyphenyl)valerate,

[0107] tert-butyl4,4-bis(4′-tert-butoxycarbonylmethyloxyphenyl)-valerate,

[0108] tert-butyl 4,4-bis(4′-(1″-ethoxyethoxy)phenyl)valerate,

[0109] tert-butyl 4,4-bis(4′-(1″-ethoxypropyloxy)phenyl)valerate,

[0110] tris(4-(2′-tetrahydropyranyloxy)phenyl)methane,

[0111] tris(4-(2′-tetrahydrofuranyloxy)phenyl)methane,

[0112] tris(4-tert-butoxyphenyl)methane,

[0113] tris(4-tert-butoxycarbonyloxyphenyl)methane,

[0114] tris(4-tert-butoxycarbonyloxymethylphenyl)methane,

[0115] tris(4-(1′-ethoxyethoxy)phenyl)methane,

[0116] tris(4-(1′-ethoxypropyloxy)phenyl)methane,

[0117] 1,1,2-tris(4′-(2″-tetrahydropyranyloxy)phenyl)ethane,

[0118] 1,1,2-tris(4′-(2″-tetrahydrofuranyloxy)phenyl)ethane,

[0119] 1,1,2-tris(4′-tert-butoxyphenyl)ethane,

[0120] 1,1,2-tris(4′-tert-butoxycarbonyloxyphenyl)ethane,

[0121] 1,1,2-tris(4′-tert-butoxycarbonylmethyloxyphenyl)ethane,

[0122] 1,1,2-tris(4′-(1′-ethoxyethoxy)phenyl)ethane, and

[0123] 1,1,2-tris(4′-(1′-ethoxypropyloxy)phenyl)ethane.

[0124] In the resist composition according to the invention, anappropriate amount of the dissolution inhibitor (E) is up to about 20parts, and especially up to about 15 parts by weight per 100 parts byweight of the solids in the composition. With more than 20 parts of thedissolution inhibitor, the resist composition becomes less heatresistant because of an increased content of monomer components.

[0125] The resist composition of the invention may include, as anoptional ingredient, a surfactant which is commonly used for improvingthe coating characteristics. Optional ingredients may be added inconventional amounts so long as this does not compromise the objects ofthe invention.

[0126] A nonionic surfactant is preferred, examples of which includeperfluoroalkyl polyoxyethylene ethanols, fluorinated alkyl esters,perfluoroalkylamine oxides, and fluorinated organosiloxane compounds.Illustrative examples include Florade FC-430 and FC-431 from Sumitomo 3MLtd., Surflon S-141, S-145, S-381 and S-383 from Asahi Glass Co., Ltd.,Unidyne DS-401, DS-403, and DS-451 from Daikin Industries Ltd., MegafaceF-8151, F-171, F-172, F-173 and F-177 from Dainippon Ink & Chemicals,Inc., and X-70-092 and X-70-093 from Shin-Etsu Chemical Co., Ltd.Preferred surfactants include Florade FC-430 from Sumitomo 3M Ltd. andX-70-093 from Shin-Etsu Chemical Co., Ltd.

[0127] Pattern formation using the resist composition of the inventionmay be carried out by a known lithographic technique. For example, theresist composition may be applied onto a substrate such as a siliconwafer by spin coating or the like to form a resist film having athickness of 0.1 to 1.0 μm, which is then pre-baked on a hot plate at 60to 200° C. for 10 seconds to 10 minutes, and preferably at 80 to 150° C.for ½ to 5 minutes. A patterning mask having the desired pattern maythen be placed over the resist film, and the film exposed through themask to an electron beam or to high-energy radiation having a wavelengthbelow 300 nm such as deep-UV rays, excimer laser light, or x-rays in adose of about 1 to 200 mJ/cm², and preferably about 10 to 100 mJ/cm²,then post-exposure baked (PEB) on a hot plate at 60 to 150° C. for 10seconds to 5 minutes, and preferably at 80 to 130°0 C. for ½ to 3minutes. Finally, development may be carried out using as the developeran aqueous alkali solution, such as 0.1 to 5%, and preferably 2 to 3%,tetramethylammonium hydroxide (TMAH), this being done by a conventionalmethod such as dipping, puddling, or spraying for a period of 10 secondsto 3 minutes, and preferably 30 seconds to 2 minutes. These steps resultin the formation of the desired pattern on the substrate. Of the varioustypes of high-energy radiation that may be used, the resist compositionof the invention is best suited to micro-pattern formation with, inparticular, deep-UV rays having a wavelength of 254 to 120 nm, anexcimer laser, especially ArF excimer laser (193 nm), F₂ excimer laser(157 nm), Kr₂ excimer laser (146 nm), KrAr excimer laser (134 nm) or Ar₂excimer laser (121 nm), x-rays, or an electron beam. The desired patternmay not be obtainable outside the upper and lower limits of the aboverange.

[0128] The resist composition comprising the polymer of the invention issensitive to high-energy radiation, has excellent sensitivity andresolution at a wavelength of less than 200 nm, especially less than 170nm, and excellent plasma etching resistance. Because these features ofthe inventive resist composition enable its use particularly as a resisthaving a low absorption at the exposure wavelength of a F₂ excimerlaser, a finely defined pattern having sidewalls perpendicular to thesubstrate can easily be formed, making the resist ideal as amicropatterning material in VLSI fabrication.

EXAMPLE

[0129] Examples of the invention are given below by way of illustrationand not by way of limitation. The abbreviations used herein are AIBN for2,2′-azobisisobutyronitrile, GPC for gel permeation chromatography, NMRfor nuclear magnetic resonance, Mw for weight average molecular weight,and Mn for number average molecular weight.

Synthesis Example 1 Synthesis of2,3-difluoro-4-tert-butoxy-a-methylstyrene/methacrylonitrile (1/1)copolymer

[0130] In a 2-liter flask, 17 g of methacrylonitrile and 56 g of2,3-difluoro-4-tert-butoxy-α-methylstyrene were dissolved in 560 ml oftoluene. The system was fully purged of oxygen, 3 g of the initiatorAIBN was added, and the system was heated at 60° C. at whichpolymerization reaction took place for 24 hours.

[0131] The polymer thus obtained was worked up by pouring the reactionmixture into a hexane/ether (3/2) mixture whereupon the polymerprecipitated. The polymer was separated and dried. There was obtained 51g of a white polymer,poly(2,3-difluoro-4-tert-butoxy-α-methylstyrene)-co-polymethacrylonitrilecopolymer.

[0132] The polymer was found to have a Mw of 16,700 as measured by thelight scattering method, and a dispersity (Mw/Mn) of 1.80 as determinedfrom the GPC elution curve. On ¹H-NMR analysis, the polymer was found toconsist of 2,3-difluoro-4-tert-butoxy-α-methylstyrene andmethacrylonitrile in a ratio of approximately 1:1.

Synthesis Example 2 Synthesis of2,6-difluoro-4-tert-butoxy-α-methylstyrene/methacrylonitrile (1/1)copolymer

[0133] In a 2-liter flask, 17 g of methacrylonitrile and 56 g of2,6-difluoro-4-tert-butoxy-α-methylstyrene were dissolved in 560 ml oftoluene. The system was fully purged of oxygen, 3 g of the initiatorAIBN was added, and the system was heated at 60° C. at whichpolymerization reaction took place for 24 hours.

[0134] The polymer thus obtained was worked up by pouring the reactionmixture into a hexane/ether (3/2) mixture whereupon the polymerprecipitated. The polymer was separated and dried. There was obtained 50g of a white polymer,poly(2,6-difluoro-4-tert-butoxy-α-methylstyrene)-co-polymethacrylonitrilecopolymer.

[0135] The polymer was found to have a Mw of 15,300 as measured by thelight scattering method, and a dispersity (Mw/Mn) of 1.67 as determinedfrom the GPC elution curve. On ¹H-NMR analysis, the polymer was found toconsist of 2,6-difluoro-4-tert-butoxy-α-methylstyrene andmethacrylonitrile in a ratio of approximately 1:1.

Synthesis Example 3 Synthesis of2,3-difluoro-4-tert-butoxy-α-methylstyrene/4-trifluoromethylstyrene/methacrylonitrile(0.6/0.4/1) copolymer

[0136] In a 2-liter flask, 17 g of methacrylonitrile, 34 g of2,3-difluoro-4-tert-butoxy-α-methylstyrene and 19 g of4-trifluoromethylstyrene were dissolved in 560 ml of toluene. The systemwas fully purged of oxygen, 3 g of the initiator AIBN was added, and thesystem was heated at 60° C. at which polymerization reaction took placefor 24 hours.

[0137] The polymer thus obtained was worked up by pouring the reactionmixture into a hexane/ether (3/2) mixture whereupon the polymerprecipitated. The polymer was separated and dried. There was obtained 55g of a white polymer,poly(2,3-difluoro-4-tert-butoxy-α-methylstyrene)-co-poly(4-trifluoromethylstyrene)-co-polymethacrylonitrilecopolymer.

[0138] The polymer was found to have a Mw of 14,700 as measured by thelight scattering method, and a dispersity (Mw/Mn) of 1.88 as determinedfrom the GPC elution curve. On ¹H-NMR analysis, the polymer was found toconsist of 2,3-difluoro-4-tert-butoxy-α-methylstyrene,4-trifluoromethylstyrene and methacrylonitrile in a ratio ofapproximately 0.6:0.4:1.

Synthesis Example 4 Synthesis of2,3-difluoro-4-tert-butoxy-α-methylstyrene/2,3,4,5,6-pentafluorostyrene/methacrylonitrile(0.6/0.4/1) copolymer

[0139] In a 2-liter flask, 17 g of methacrylonitrile, 34 g of2,3-difluoro-4-tert-butoxy-α-methylstyrene and 30 g of2,3,4,5,6-pentafluorostyrene were dissolved in 560 ml of toluene. Thesystem was fully purged of oxygen, 3 g of the initiator AIBN was added,and the system was heated at 60° C. at which polymerization reactiontook place for 24 hours.

[0140] The polymer thus obtained was worked up by pouring the reactionmixture into a hexane/ether (3/2) mixture whereupon the polymerprecipitated. The polymer was separated and dried. There was obtained 55g of a white polymer,poly(2,3-difluoro-4-tert-butoxy-α-methylstyrene)-co-poly(2,3,4,5,6-pentafluorostyrene)-co-polymethacrylonitrilecopolymer.

[0141] The polymer was found to have a Mw of 13,200 as measured by thelight scattering method, and a dispersity (Mw/Mn) of 1.66 as determinedfrom the GPC elution curve. On ¹H-NMR analysis, the polymer was found toconsist of 2,3-difluoro-4-tert-butoxy-α-methylstyrene,2,3,4,5,6-pentafluorostyrene and methacrylonitrile in a ratio ofapproximately 0.6:0.4:1.

[0142] Evaluation of Polymers

[0143] The polymers obtained in Synthesis Examples (SE1 to 4) weredetermined for transmittance.

[0144] A polymer, designated Comparative Polymer 1, was synthesized froma monodisperse polyhydroxystyrene having a molecular weight of 10,000and a dispersity (Mw/Mn) of 1.10 by substituting tert-butyl groups for30% of the hydroxyl groups. Comparative Polymer 2 was poly(methylmethacrylate) having a molecular weight of 15,000 and a dispersity of1.7. Comparative Polymer 3 was a novolac polymer having a meta/pararatio of 40/60, a molecular weight of 9,000 and a dispersity of 2.5.

[0145] Polymer transmittance measurement

[0146] Each polymer, 1 g, was thoroughly dissolved in 10 g of propyleneglycol monomethyl ether acetate (PGMEA), and passed through a 0.2-micronfilter, obtaining a polymer solution.

[0147] The polymer solution was spin coated onto a MgF₂ substrate andbaked on a hot plate at 100° C. for 90 seconds, forming a polymer layerof 300 nm thick on the MgF₂ substrate. Using a vacuum ultravioletspectrometer (VUV200S by Nihon Bunko K.K.), the polymer layer wasmeasured for transmittance at 248 nm, 193 nm and 157 nm. The results areshown in Table 1. TABLE 1 Transmittance (%) Polymer 248 nm 193 nm 157 nmSE1 Polymer 88 15 30 SE2 Polymer 88 16 28 SE3 Polymer 87 18 33 SE4Polymer 89 20 31 Comparative Polymer 1 85  1  3 Comparative Polymer 2 9070  1 Comparative Polymer 3 70  1  6

[0148] Dry etching test

[0149] Dry etching tests were carried out by spin coating the abovepolymer solution on a silicon substrate, baking on a hot plate at 100°C. for 90 seconds to form a polymer layer of 300 nm thick on the siliconsubstrate, and etching the polymer layer under two sets of conditions.The results are shown in Table 2.

[0150] (1) Etching test with CHF₃/CF₄ gas

[0151] Using a dry etching instrument TE-8500P (Tokyo Electron K.K.),the difference in polymer film thickness before and after etching wasdetermined.

[0152] The etching conditions are given below. chamber pressure 40.0 PaRF power 1300 W gap 9 mm CHF₃ gas flow rate 30 ml/min CF₄ gas flow rate30 ml/min Ar gas flow rate 100 ml/min time 60 sec

[0153] (2) Etching test with Cl₂/BCl₃ gas

[0154] Using a dry etching instrument L-507D-L (Nichiden Anerba K.K.),the difference in polymer film thickness before and after etching wasdetermined.

[0155] The etching conditions are given below. chamber pressure 40.0 PaRF power 300 W gap 9 mm Cl₂ gas flow rate 30 ml/min BCl₃ gas flow rate30 ml/min CHF₃ gas flow rate 100 ml/min O₂ gas flow rate 2 ml/min time60 sec

[0156] TABLE 2 CHF₃/CF₄ gas etching Cl₂/BCl₃ gas etching Polymer rate(nm/min) rate (nm/min) SE1 Polymer 92 120 SE2 Polymer 93 125 SE3 Polymer91 106 SE4 Polymer 98 108 Comparative Polymer 1 110  210 ComparativePolymer 2 180  350 Comparative Polymer 3 90 110

[0157] Using the above polymers, resist compositions were prepared asfollows.

[0158] Examples and Comparative Example

[0159] Resist solutions were prepared by thoroughly dissolving thepolymer, photoacid generator (PAG1 or PAG2), basic compound anddissolution inhibitor (DRI1) in the solvent in the amounts shown inTable 3 and passing the solutions through a 0.1-micron PTFE filter.

[0160] Note that the PGMEA solvent contained 100 ppm of fluorochemicalsurfactant FC-430 (Sumitomo-3M Co., Ltd.).

[0161] On silicon wafers, DUV-30 (Nissan Chemical Co., Ltd.) was coatedto form films of 55 nm thick so that the reflectance to KrF light (248nm) was reduced below 1%. On the coated substrates, the resist solutionswere spin coated, then baked on a hot plate at 100° C. for 90 seconds togive resist films having a thickness of 300 nm.

[0162] The resist films were exposed by means of an excimer laserstepper (NSR-S202A, from Nikon Corporation; NA 0.6, σ 0.75, 2/3 annularillumination). Immediately after exposure, the resist films were bakedat 110° C. for 90 seconds and then developed for 60 seconds with a 2.38%aqueous solution of tetramethylammonium hydroxide, thereby giving 1:1line-and-space patterns.

[0163] The resulting resist patterns were evaluated as described below.The results are shown in Table 3.

[0164] Evaluation:

[0165] The exposure dose which provides a 1:1 resolution at the top andbottom of a 0.25-μm line-and-space pattern was the optimum exposure dose(sensitivity Eop). The minimum line width of a line-and-space patternwhich was ascertained separate at this dose was the resolution of a testresist. TABLE 3 Photoacid Basic Dissolution Polymer generator compoundinhibitor Solvent Eop Resolution (pbw) (pbw) (pbw) (pbw) (pbw) (mJ/cm²)(μm) SE1 PAG1 TBA — PGMEA 30 0.24 (100) (2) (0.1) (1000) SE2 PAG1 TBA —PGMEA 20 0.22 (100) (2) (0.1) (1000) SE3 PAG1 TBA — PGMEA 24 0.22 (100)(2) (0.1) (1000) SE4 PAG1 TBA — PGMEA 28 0.24 (100) (2) (0.1) (1000) SE1PAG1 TEA — PGMEA 32 0.24 (100) (2) (0.1) (1000) SE1 PAG1 TMMEA — PGMEA27 0.24 (100) (2) (0.1) (1000) SE1 PAG2 TBA — PGMEA 22 0.24 (100) (2)(0.1) (1000) SE1 PAG1 TBA DRI PGMEA 28 0.24 (100) (2) (0.1) (10) (1000)

[0166] As is evident from Tables 1 to 3, resist materials using thepolymers of the invention have sufficient transparency around thewavelength of F₂ excimer laser (157 nm) and satisfy the resolution andsensitivity on excimer laser exposure. The difference in resist filmthickness before and after etching is small enough, indicatingsatisfactory dry etching resistance.

[0167] Japanese Patent Application No. 2000-271189 is incorporatedherein by reference.

[0168] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A polymer comprising recurring units of the following general formula(1):

wherein R¹, R², R³ and R⁵ each are independently hydrogen, fluorine, ora straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to20 carbon atoms, R⁴ is an acid labile group, letters a, b and c arenumbers satisfying 0≦a<5, 0≦b<5, 0<a+b<5 and 0<c<5, and m and n arepositive numbers.
 2. A resist composition comprising the polymer ofclaim
 1. 3. A chemically amplified, positive resist compositioncomprising (A) the polymer of claim 1, (B) an organic solvent, and (C) aphotoacid generator.
 4. The resist composition of claim 3 furthercomprising (D) a basic compound.
 5. The resist composition of claim 3further comprising (E) a dissolution inhibitor.
 6. A process for forminga resist pattern comprising the steps of: applying the resistcomposition of claim 2 onto a substrate to form a coating, heat treatingthe coating and then exposing it to high-energy radiation having awavelength of up to 300 nm or an electron beam through a photo mask, andoptionally heat treating the exposed coating and developing it with adeveloper.